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B&W TV Murphy V410

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PYE625
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It is usually the case that a set could be almost anywhere in the country and sheer distance can make it unviable. How often is it the case where a set becomes available that is located in the next street and is within walking distance? Not that often I bet.

Well this one was and although I don't really want another set, I simply could not say no in this instance. After 50 quid changed hands, it is now residing in my rather cluttered workshop.

So here we are, after a very long and tedious hot journey of a few hundred yards, some photo's of the set....

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She was obtained from an antique shop around ten years ago in Norwich and cherished as an ornament by the former owner's in their most attractive 50's styled home. It is therefore probably safe to assume that the set was used during it's service life in the Norwich region, the tuner frequencies will confirm this later however.

To understand the black art of electronics is to understand witchcraft.
Andrew.

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Topic starter Posted : 17/07/2021 12:08 pm
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Cathovisor
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@pye625

Best of all Andrew, is that it still has its mains connector, which is often missing.

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Posted : 17/07/2021 12:35 pm
PYE625
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That is very true Mike, you are right there. 👍

Looking over the chassis, it would appear to me that the set has not been opened since it left the factory. There is no evidence of any work or disturbance to be found. Even the label from the CRT was lying neatly at the bottom of the case, so must have fallen off at some point.

The only minor thing missing is a "volume" ident that is probably very similar to the "channel" ident in the last photo below. Anyone got one they can spare? 😉

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To understand the black art of electronics is to understand witchcraft.
Andrew.

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Topic starter Posted : 17/07/2021 12:38 pm
PYE625
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As for the oil filled line output transformer, it would seem not to have leaked oil. There is a slight amount on the EHT recifier base cover, but it must have seeped down inside the tubing. Nothing to be concerned about though. The real concern is if it is still operational of course.

Anyway, it's too hot to mess around with it today. I think just a gentle vacuum and brush out of the dust will suffice for the time being. Besides, after that epic long journey to collect the set, one is mildly worn out. 😊

To understand the black art of electronics is to understand witchcraft.
Andrew.

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Topic starter Posted : 17/07/2021 12:43 pm
PYE625
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After some squeezing and manipulation, I manage to get the B&K onto the CRT base long enough to establish that the CRT at least will be respectable.

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More views of the line output valves plus a less than healthy wax capacitor to the right.

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To understand the black art of electronics is to understand witchcraft.
Andrew.

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Topic starter Posted : 17/07/2021 2:09 pm
Cathovisor
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I think you'll find that'll produce a splendid picture, bearing in mind what we saw with the VT161 and the B&K readings on its tube.

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Posted : 17/07/2021 2:23 pm
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Katie Bush
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I like these!

I owned a V410 back in the '70s, collected from a family about a quarter mile from home, and brought home on my kid brothers' 'soapbox cart' - We are talking around '71~'72!!   That set worked straight off the cart, and even came in handy when my parents' (living room) telly went cat-o-wompuss during the Christmas holidays one year. I still had it up to VHF shutdown, then my dad decided it was time to heft it into the "ash wagon" at York station. I was gutted, and more than just a bit angry, and all he could say was "It's no good to you, they've turned that lot off now" - I replied with something like "But you never know what the future might bring" - His answer "Well you don't think they're going to turn it all back on again do you?". . . . . I think he missed the point, but here we are, restoring these things to working order almost forty years later!

From the same place, we acquired a Bush TV80 which became my brother's bedroom telly, and V216C, with CRT down to atmosphere. Which I kept in the hope of finding a CRT for it - I never did, but about three years ago I did actually find a complete V216C, which came home in the back of my Volvo V70 - A somewhat more glamorous soapbox cart!

Let's just say, if I can find one, I want a V410, just compliment my V310.

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Posted : 17/07/2021 3:52 pm
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PYE625
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I have removed and cleaned the CRT plus re-affixed the fallen label. A simple wipe with a barely damp cloth was all that was needed here. No nasty nicotine stains to remove either.

The chassis was lightly brushed and the wosrt of the dust vacummed up. Is that spelt right, it looks wrong. Ok, hoovered up.... there, that's better.

Oh, and the LOPT had a bit of a clean too but may have to be removed to gain easier access to a couple of wax capacitors.

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To understand the black art of electronics is to understand witchcraft.
Andrew.

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Topic starter Posted : 17/07/2021 5:18 pm
PYE625
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I have removed the LOPT can (having made careful notes of the connections) for the purpose of easy access to C103, the 0.25uf boost HT capacitor which has suffered from a wax meltdown at some point. The LOPT itself has had a clean whilst it is out of the chassis. This is all very well assuming it works of course. But we must not allow doubts to prevail, otherwise we would never do anything.

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To understand the black art of electronics is to understand witchcraft.
Andrew.

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Topic starter Posted : 17/07/2021 8:54 pm
Katie Bush
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Posted by: @pye625

. The LOPT itself has had a clean whilst it is out of the chassis. This is all very well assuming it works of course.

Funnily enough, I've always been given to believe that these LOPTs "never" fail - Well, extremely rarely!

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Posted : 17/07/2021 9:10 pm
PYE625
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I have a feeling that this one would almost certainly fail, or give problems, if powered up at the moment.

The reason is that I can measure a leakage of nearly 570 megs between the EHT rectifier heater winding and the earthy winding. Similarly, just over 100 megs between the other main windings and ground. This is at 500vdc. Not a good sign. Imagine 15KV.

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I am hoping this is due to moisture ingress and that by removing the bung and passing a small current through the whole winding the moisture can be driven off. It could take some time, but this must be done for obvious reasons.

I had a similar issue with my Murphy V280C LOPT here....

https://www.radios-tv.co.uk/community/black-white-tvs/murphy-v280c/paged/2/

To understand the black art of electronics is to understand witchcraft.
Andrew.

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Topic starter Posted : 17/07/2021 10:16 pm
PYE625
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The current passing through the total winding is 19v at 225mA. This is just over 4 watts. The case has become just warm to the touch after about an hour. The leakage has increased. The resistance now at 500v is about half what it was when cold.

Interesting that. What can happen to the picture on a set with a LOPT overwind with poor insulation? As it becomes warmer, the picture balloons out as the EHT drops due to increasing leakage.

In any case, I will leave the LOPT warming through and simply hope it will begin to show lesser leakage. Has to be worth a go.

To understand the black art of electronics is to understand witchcraft.
Andrew.

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Topic starter Posted : 17/07/2021 11:29 pm
PYE625
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Bubble bubble, toil and trouble....

After leaving the current flowing overnight, the leakage resistance has now decreased still further. It is approximately a tenth of when the LOPT was cold. The can is quite warm, but not excessively so.

I am expecting it to take some days, if not weeks, for any moisture to be driven off. It has to migrate through the oil. It got in there, so surely must come out? Well we will see. It is a bit of an experiment to be honest.

To understand the black art of electronics is to understand witchcraft.
Andrew.

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Topic starter Posted : 18/07/2021 8:54 am
PYE625
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Turning attention back to the chassis, it is only too evident the superb build quality and engineering behind this and indeed most other Murphy designs up to the period. Access to some components may be tricky, but servicing a vintage Rolls Royce is never easy I can well imagine. Yes, the LOPT could have been slightly better but there would have been a limit to cost at the time.

I will gradually proceed with re-stuffing the wax capacitors and re-forming the electrolytics. Even if the LOPT fails to give satisfaction, I am confident even this can be repaired if required.

Here below is the mains selector panel partially removed and then looking down behind the scan coil assembly. Again, large accumulations of dust have been brushed out and sucked up. The fins of the rectifier can be dusted out with a feather. Just need to find a willing bird happy to donate such an item.

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To understand the black art of electronics is to understand witchcraft.
Andrew.

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Topic starter Posted : 18/07/2021 11:07 am
PYE625
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I have downloaded the comprehensive 43 page Murphy service manual from UKVRRR (at £1.99 it's well worth it), but as simplified information is contained in the 1959-60 R&TV servicing book, page 457, I will refer to that when required. The circuit component references are the same anyway. Other data sheets may well differ of course.

To understand the black art of electronics is to understand witchcraft.
Andrew.

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Topic starter Posted : 18/07/2021 11:24 am
PYE625
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Earlier this evening I re-stuffed the previously pictured C103 boost HT capacitor, plus C104 next to it, the line scan coupling capacitor. I also cleaned up the mess of leaked wax and crud in that area.

Whilst I had open the mains voltage selector panel (pictured above), I took the liberty of re-stuffing C31, video to CRT cathode coupling, plus C92 between the frame linearity preset controls. One thing I forgot to check for is a modification listed in the service manual to install a 1 meg resistor in the earthy end of the focus control preset. Presumably, they must have had cases where this control failed or burnt out. "NOTE. This resistor must be added to any receiver which has not already been modified" they say.

To understand the black art of electronics is to understand witchcraft.
Andrew.

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Topic starter Posted : 18/07/2021 10:24 pm
Jayceebee
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Posted by: @pye625

One thing I forgot to check for is a modification listed in the service manual to install a 1 meg resistor in the earthy end of the focus control preset. Presumably, they must have had cases where this control failed or burnt out. "NOTE. This resistor must be added to any receiver which has not already been modified" they say.

I’m not sure if that was the cause but I do remember a couple of sets coming into the workshop with the whole mains selector panel completely burned up.

John.

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Posted : 19/07/2021 2:41 pm
PYE625
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I can imagine a poor connection on the mains selector could cause arcing and the plastic dial to warp and melt maybe.

The 1 meg resistor is fitted to this set, inside some sleeving.

To understand the black art of electronics is to understand witchcraft.
Andrew.

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Topic starter Posted : 19/07/2021 5:52 pm
Jayceebee
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@pye625 Well that was my thoughts also, a lot of heat around there and not the best materials that we have today. i can remember the plastic disc which rotated becoming very discoloured on a lot of sets. Always liked the V410 and they had a little trick up their sleeve, with a good signal if you set the contrast at maximum the video would completely invert to negative without loss of sync.

John.

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Posted : 19/07/2021 7:38 pm
PYE625
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That would be interesting to see, assuming I can of course return the set to working order.

The biggest challenge I can see will be the LOPT. The measured leakage has not come down very much and if there has been internal EHT tracking, then of course it never will no matter how long it is kept warm.

A good example of internal EHT tracking may be seen here in Nick's interesting thread over on UKVRRR...

https://www.vintage-radio.net/forum/showthread.php?t=150608

I really do not want to open up the can so will give it every chance to dry out any possible absorbed moisture as described previously.

To understand the black art of electronics is to understand witchcraft.
Andrew.

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Topic starter Posted : 19/07/2021 8:38 pm
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